A torque converter includes an impeller and a turbine, and transmits a torque from the impeller to the turbine through hydraulic oil contained in the interior thereof. The impeller is fixed to a front cover to which the torque is inputted from an engine. The turbine is disposed in opposition to the impeller within a fluid chamber. When the impeller is rotated, the hydraulic oil flows from the impeller to the turbine. The flow of the hydraulic oil rotates the turbine, whereby the torque is outputted.
Additionally, the torque converter includes a lock-up device. The lock-up device includes a piston. When the lock-up device is turned on, the piston is engaged with the front cover. As a result, the torque from the front cover is inputted to the piston. The torque is mechanically transmitted to the turbine from the piston, and is then outputted therefrom to an input shaft of a transmission.
For example, a torque converter described in Japan Laid-open Patent Application Publication No. 2010-53963 is provided with a clutch part in the outer peripheral part of a turbine shell. The clutch part is composed of a coupling member, a friction block and a piston. The coupling member and the friction block are provided on the turbine side. The piston is provided with a friction member fixed to the outer peripheral part thereof, and is axially movable. Additionally, when the piston is moved to the turbine side and thereby the friction member is pressed onto the friction block, a lock-up on state (a torque transmission allowed state) is made.